In a state where a tire contacts the ground, tubular space is formed by a main groove extending in the tire circumferential direction and road surface. The rotation of tires lets air compressed in the tubular space to release outside, and as a result, air columnar resonance noise is generated. Since the air columnar resonance noise is offensive noise whose frequency is around 1 kHz, reduction in air columnar resonance noise has been demanded conventionally. For example, the pneumatic tire disclosed in the patent document 1 has a great number of oblong holes extending in the depth direction of a main groove formed in a sidewall of the main groove. By the oblong holes, friction resistance against the air flow in the main groove is increased, resulting in reduction in air columnar resonance noise.
Patent Document 1: Unexamined Japanese Laid-Open Patent Publication No. 10-315711 (FIG. 1)